Fig. 1: Schematic representation of the reaction-diffusion system.

a Reaction scheme with involved species and b reaction-diffusion event after injection of ProA and IN at a point. Here, distant zone becomes basic in pH due to enzymatic conversion of ProA to A, resulting in activation of Kemp Elimination reaction (i.e., conversion of NBI (R) to CNP (P)). Due to the presence of acidic inhibitor in the nearby zone, the reaction is suppressed. Slower diffusion of IN in the gel is due to binding with nanoparticles embedded in gel. c Schematic of the reaction set up with components (urea as ProA and ATP as IN) and reaction schemes. At the empty circular zone (5 mm diameter) aqueous solution of (ATP + urea) or (ATP + NH₄HCO₃) were added and allowed to diffuse into the agarose gel matrix (0.75 wt%). Experiment with the addition of (ATP as IN + NH₄HCO₃ as A) has been done as control experiment, to check the direct effect of A + IN. Blue and red arrow indices faster and slower diffusion of urea and ATP through gel matrix, due to non-binding and binding of GNP, respectively. The gel is embedded with CTAB-capped GNP (0.2 nM), urease enzyme (15 nM) and NBI (0.5 mM).